Liquid crystal display devices, by virtue of their low power consumption, low production costs, light weight and low profile feasibilities, ready color display capabilities, and other advantageous features, have come to be employed for the increasingly further diversified applications of late.
The liquid crystal display device is usually configured of a pair of substrates each having an electrode layer and alignment layer, and a liquid crystal substrate sandwiched and sealed therebetween.
Known alignment layer forming methods include the vacuum evaporation depositing process, rubbing process, and various other techniques, of which the vacuum evaporation depositing process serves particularly advantageously to form the super-twisted type of liquid crystal display devices having a large liquid crystal molecular twist angle ranging from 180.degree. to 360.degree. (Japanese Patent O.P.I. Publications Nos. 107020/1985 and 203921/1985) for example, by virtue of a relatively large pretilt angle (formed by the direction of liquid crystal molecular directors in contact with the alignment layer surface of a substrate and the substrate surface) that the process provides.
Conventionally, the following vacuum evaporation depositing methods have been known to be employed for forming the alignment layer of liquid crystal display devices:
(1) A method that uses a point source for the evaporation source PA1 (2) A method that applies an iris-controlled vapor particulate beam to the substrate being slide-shifted in the process in a vertical attitude to the evaporation depositing direction (Japanese Patent O.P.I. Publications Nos. 5232/1986 and 24864/1979). PA1 (3) A method that, by using a specifically formed slit through which to transmit depositing vapor particles, vertically slide-shifts the substrate in a warped posture (Japanese Patent O.P.I. Publication No. 5232/1986).
By method (1) above, however, the closer to the end of a substrate, the greater will deviations be between the actual depositing direction and an anticipated one, although in a central area of the substrate, such deviations may be minimized and high accuracy depositions made in the anticipated direction. Accordingly, the resultant alignment angle of a liquid crystal display device will vary, depending on the local substrate area, and in consequence, the contrast ratio, threshold voltage, and other substrate parameters will be disuniformized, raising a problem of degraded display capabilities.
By method (2) above, as described in Japanese Patent O.P.I. Publication No. 5232/1986, since the substrate is slide-shifted in a vertical attitude to the evaporation depositing direction, the evaporation depositing directional angle may be uniformized but the evaporation depositing angle and layer thickness will tend to be disuniformized, rasing a problem of as yet insufficient display capabilities.
By method (3) above, as described in Japanese Patent O.P.I. Publication No. 5232/1986, since a specifically formed slit is employed and the substrate slide-shifted vertically to the evaporation depositing direction in a warped posture, an alignment layer may be formed with its evaporation depositing directional angle, evaporation depositing angle, and layer thickness all duly uniformized, but on the other side of the coin, the method requires manufacturing equipment of considerable complexity for its implementation, raising a problem in the difficulty of its commercialization.